I have recently developed a theory for explaining how most microbes attain their shapes; New murein is covalently linked to the stress-bearing wall by the bacteria in such a way that cleavages needed to permit enlargement of the cell transfer the stress to the new murein. There are a number of strategies used by different organisms to achieve this end. So far the theory can account for coccal and rod-shapes of both Gram-positive and -negative bacteria and is beginning to account for the more complex shapes such as stalked and budding bacteria. The theory is compatible with available data. We will measure the degree of stretch of the walls in growing organisms above their stress-free state. This will be done by direct phase microscopy on filaments and chains by watching shrinkage when cytoplasmic membranes are breached in a variety of ways. It will also be measured by rapid flow narrow beam turbidity following changes after osmotic pressure of the medium is changed. Because shrinkage due to relaxation of the wall in hypertonic medium is much faster than plasmolysis, the two processes can be separated. Plasmolysis can be accelerated with small amounts of ultrasound. Second, by rapid flow turbidity we will measure the internal osmotic pressure which can be calculated from the largest external osmolarity that does not lead to plasmolysis in the presence of ultrasound. These types of measurements will first be made with strains of E. coli, including strains with a defect in potassium transport to prevent them from accumulating this cation to compensate for osmotic challenge. Because the theory makes definite predictions, it can be critically tested by the proprosed measurements. For example, the ratio of in vivo stretched wall area of the cell to unstretched area should be about 2 for E. coli and B. subtilis but only a little greater than 1 for S. faecalis. The stretch and osmotic pressure measurement will then be extended to a range of types of bacteria. The new theory accounts for the growth, division, and shapes of most organisms without contractile proteins whose wall supports an osmotic stress; we shall extend the theory further. At present it does not accomodate curved, helical cells which do not seem to have a basically helical structure to the wall polymer. The theory has important implications for control of microbial growth.